Multichannel radioelectric communication system



H. CHIREIX Feb. 23, 1954 2 Sheets-Sheet 1 Filed NOV. 24, 1950 V #s 1 lllllllllllll I I f Nm ,o u@ vixu xum @MMR Mw uv Kum vwkk S VEB -if D ,kwh Qu .USF T .35.6

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MULTICHANNEL RADIOELECTRIC COMMUNICATION SYSTEM I Feb. 23, 1954 Filed NOV. 24, 1950 2 Sheets-Sheet 2 N mw Patented Feb. 23, 1954 RADIoELEoTmc COMMWICATION ySYSTEM Hem-i chireix; rarisrrrce, assigii tt 'sbcif France Francaise Radio-Electrique, aA corporation of cimiteriali 19st, 'serai 'rivets claims pricritygapiilitti'ir France December 2, 1949 'rhecipiect tiiiierirsqiitiiietin is the soni-y tion of the following problem: W

A Certain number @i arbitrarily rlae 91151 operating on ultrashor Waves. ansi forml ng' a network., have t simultanouslrpretense,.12- tweeri themselves a certain nrrrilelf @Ermelcatiohspf varied nature. svrrisroniegdifferent'srvices 9 11 @hacerle ease. fine staresterized by a wave having an ultra-high fre- These communications are mostly telephone conversations but mayalso be of another nature (@g-I telesraphvrfecsimileial It is n the Qtherhand dsiredtiietiee were of the band eecupiedv the netwerk the, Smallestrossile and: it id esrid that serial transmitters will never function in the same Several transmitters max hevrever-epei1te Sfrilteiislv but diereiit. Chanels an@ therefore@ transmitter. Qreretiris e i r 1 number of channels iniiuencesthe local receiver listening. .011' @maternels-, ,r The preblfmtf be Solved is therefore different from that wher e a singlemltiple connection is prvgeiitetveeln@ ielietieraand. latter problem las alreedmesc @eelt withiir French Patent No. 932,420 iiled August 2 0 19g@ The object of the present invention is the preceding to affordr a ifore complete solution of the problem mentioned hereinabove.

Itis obvious that diiiculties arise atl the reception of a channel subject to violent interferences due to local emissions injother channels As the a'erials should be non-directional^ so, that the network can spread in all directions it not possible to uncouplethe receiving -and transmitting aerials', toa great itt'ir ai station and the electric Held du'e to local interference may excd by 80 decibels or more the useful eld for rel ceiving the distant stations: -Further, since the emissions of different cl'rannelsv are comprised in a restricted frequency interval, that is to say, a relatively narrow band for all the channels; it cannot be: expected to attain directly by the use( of ultra-high frequency a selectivity sufficient for excluding local interference;

It is therefore necessary at the receiving end to changey the' frequency so as to lower the frequency of the whole of the channels in such a way as to obtain a muchV greater relative' band Width, allowing a selection at the intermediate frequency;

Nevertheless:v due to nonlinear distortion-plie# no'rnena` the twol following troublsme* eict are produced:

s citrus; (ci. it-'iti (1.) An intermoduidtion erreur mixing thev modulationof one or several interfering signals with th signal to be receivd.

(2v-i.) The creation of parasitic frequencies Ain the occupied band as' soon as two or more local signals interferewith one another.

Finauy if,-A as ii is recomended in the 'patent heretofore mentioned, the different emitted waves corresponding t o tl 1 e different channels are produced by interinetliV te'y frequencies transposed in groups in the ultra-high frequency spec tr'ur according to the technique if single' band transmitters, the same causes of non liri ri 'undat the mission in additiorithe agated Waves are effected' with transrnbdirla# tions bylnareiti raieset Sneller amplitude in the interiorof the occupied band.

According to the patent iireidfcr rrieritiedthe effects' of intermodulatin are avoided by providing diffrent iridd'uidtitri frequenties rer the different channels. `T o this end, the different channels are modulated by speech currents transposedin the dieret 'spectrums according ui the technique of carrier currents 'riiisviis trie re'su'u thai-en the receiving rid after 'rplil ricarica arid detenuta df the intermediate qderiey ccrrespondirig id this charmer t medication tarif be eliminated j; in the band filter corresponding to the transposition "frequency ofv said channel. This is supplemented according to theprsnt invention by means havingprincipallyth 0nd point for its Objict; that 's" tO sali the para-v siiic waves affecting the band; and their hdrr'r'i'- fuieffeii.

The parasitic waves affecting' tire tand are r-y 'duced as to their level and the numberv df tir s parasitic wavestliat can ter:

iisir narmruierfeercdir be rdiiced by r have irrrrrifuij taratit-rain@ tir-wen kiidwn consider iiiiar characteristic df tiri fo'rr:

ri'it''cri rent exists; and that the signal to b'e' in frequency isisuiierpnsd thereto: Theiii @suV where 3 sion linear frequency changing signifies therefore that in the case of several applied signals no combinations are formed that are due to these signals.

In the case of several sinusoidal signals of different frequencies X will have the form:

Xi|-X2+X3+.

and it results that for a term such as L"y" con- Y tains components of frequencies such as: y iffiisfzifs subject to the condition r-l-s-l-"tzp If all the signals are grouped in a relatively narrow part of the band, the terms ofeven power are incapable of causing parasitic frequencies being either considerably above or considerably below the useful band.

The characteristic to be considered becomes therefore:

If the relative width lof the band is not narrow certain terms of even power should be considered.

In particular if the development of the expression is limited to ve terms, (1) can be replaced by im 3 2 fmin l (fmax and imm being the maximum and minimum frequencies.

The two relations resulting into of the eiects of the term da:4 are:

If these relations are satisfied the effect of the term w12 can also be neglected due to the fact that it leads to the easier condition It is therefore essential that this first condition, is satisfied with respect to the intermediate frequencies occurring in emission if the ultra-high frequency transmitter is of the single band kind.

Furthermore it is necessary that the combinations due to the term e115 and the following terms are negligible. v

It is seen that without regard to the magnitude of the coefficients, these terms decrease very rapidly when the levels diminish, so that a reduction of decibels of the general level involves a level reduction of 50 decibels for the term e while the reduction is 10 decibels only for the useful term aw.

Therefore it is seen that the combinations due to the term e335 and a portion to the following terms can be rendered absolutely negligible by adoption of the system of amplitude modulation consisting in only keeping oneside band and attenuating the carrier. This is rendered possible due to the fact that the modulations are transposed in frequency and that consequently the side bands are situated sufficiently distant from the carriers. A carrier reduction of the order of 10 decibels leads for the terms e125 to a reduction of parasitic waves due to beats between carriers by 50 decibels; however, in principle no reduction of beats of side bands between'one another is (odd terms) (2) the suppression` 15, within the useful band, the resultant frequenciesI represented by Equation 1. It results from these considerations that Equation 1 can betransformed into y=ax+c3 (3) am being the useful term and cm the harmful term. The different 'channels are distributed in the occupied band in such a way that the parasitic f frequencies due to combinations introduced by this term differ at least by a unit frequency difference from any of the useful frequencies. They can then be entirely eliminated due to the selectivity of the intermediate frequency stages'of the receivers.

The undesirable frequencies created by the term cm3 can result from the interference of any two interfering channels which give rise to frequencies Zizifi. If all the frequencies are comprised in a restricted band that is to say if the relative width of the band is small, only the frequencies' 2jr-fi need be considered as these alone give a frequency in the band or in the neighbourhood thereof.

Y For a multiplex of m channels the number of these undesirable frequencies is m (1n-1) as each y channel can be associated with the (1n-1) other channels, m' being the total number of channels.

The spectrum occupied by these undesirable frequencies extends from fmin=(fmx-fminl to fmX-i-(fmaX-fmin) therefore it verifies a band Width equal t0 3(max-min) =3A max and min denoting the maximum and minimum frequencies,

respectively, and Af the useful band. Thus, the spectrum occupied by these m (1n-1) waves spreads over three times the useful band.

Undesirable frequencies can also result from the interference of three channels with one another. The number of possible combinations is that of objects taken in sets of 3 among m objects, therefore Furthermore, with each combination the parasitic frequencies ifiifzifs can be associated. If however, only the frequencies falling into the band or its vicinity are considered, the frequencies to be associated with each combination are The number 'of parasitic frequencies is therefore This number of combinations of three fre- 1 quencies is larger than the number of combinaamplified. But for these beats the average percentage of modulation of the different channels at a given moment must be taken into account and it is sufficient that this average percentage` is itself 10 decibels lower than the maximum rate tions of two frequencies when m is larger than 4. Nevertheless, all these combinations give rise to frequencies which are partly identical.

The problem consists therefore in distributing `judiciously the different channels in the occupied band in such a way that the parasitic frequencies never consider with the position of a channel. This means to determine the frequency distances between consecutive channels, the sum of all these frequency distances corresponding tov the total band.

It. is convenient to4 define a unit of frequencydifference termed hereinafter' the predetermined frequency difference; If the frequency distance between any two consecutive channels is an integral multiple of this. predetermined frequency difference, the total band will also be a multiple of this predetermined frequency difference. The diiferent channels can be donned by numbers. which will be integers and if' the.` number of the fhst channel is zero, the. number. off-the lastV one. will be S, S. being an integer representing the. sum of all' the frequency distances. The. total useful band will thus be defined' by S-l-l and divided inta Si equal intervais.

Furthermore, the. parasitic frequencies givenl by4 additions or subtracticns of numbers coincide exactly with one or the other of the. integers. They therefore coincide exactly with a channel or differ from the same 'by' one or more predetermined frequencyy differences.

In order to avoid' interference frequencies fallon a non occupied channel, the frequency distances between two successive channels must be different multiples of 'the predetermined fre-v quency difference. S must be sufficiently high 25 so` that. the parasitic frequencies can nd their place. at. the numbers unoccupied by the channels. It is obviously preferable tomake S as. small as possible in order to obtain for a given total. band the largest possible predetermined frequency' difference.

Infact, asv has been mentioned heretofore the combinations areL not all distinct and it is noted that conmination of two frequencies add practicalflyf no new number to combinations of three frequencies, a certain number of which are, by the way, comm-on. Further, all these combina-y tions are more or less uniformly distributed between the value -S- and the value |2S, that is to say in the interval 3Af so that the number of combinations in the interval of 0 to S is practicallly at thev utmost equal to 'Ifhereforee the. value S. (multiplev of m-Dl must'. therefore be at least of the order of 50 inA order to reserve the, freeV numbers corresponding, to. the channels'.

Ifc the; number of not;` distinct combinations increased itA Willbe sumeient, to choose an in.- tegralmultiple of (.m,-1). near to 2. mim Dm )l Eight channels.; therefore. lead. to. S263: or. S.=.5.6 0

p-l-(m-Zl andtheisum of the frequency distances is:

6 receiver receiving the higher l 6i' y y Taking into account the two values' of S heretofore defined p is equal to the integer equal to or immediately following:

or this integer augmented by a unit.

Thus for: m=8 p is found tov equal. 5 or (i, and 5 is in fact sufficient;` m=6 p is found to equal 2 cr 3, and in fact 3 should be chosen.

For m=12 p is found to equal 15 or 16if 15 is adopted, the smallest frequency distance ist: 1-5 times the predetermined frequency difference and the largest frequency distance equals 25 times the predetermined frequency difference.

The. occupied band will have ay width being 22()E times the predetermined frequency diierenceh 'lihe order in which the. different frequency' distances: should betaken seems. rather arbitrary.

Therefore a law has been. established for the.- distributicn of channels in the. occupied bandi. e.V for the. frequency distances between successive channels as different. integer numbers, the smalle. est and the largestv of which determined by the numberA of channels, all the: integer numbers; comprised between. theseA twolimits.v being uti lized, this new distribution having as an object; the rejecting of interferences: the. amplitude off which cannot be neglected.

In these conditions the parasitic frequencies of non negligible amplitude can be very much weakened at the reception in the intermediatefrequency stagesv ofthe receivers` by the selec:u tivity thereof.

It is to be noted that according tothe` arrangement provided in the patent heretofore men tioned and consisting in having diiferent fire-1 quency modulations for different. channels, their amplitudeL after intermediate frequencyr ampli fying stages can remain high withoutinconven-r ience. for the operation. l

According to an arrangement being difieren-tfl from that of' the patent heretofore mentioned, it is preferred to use two receivers at reception,K fed by the same aerial, each of the receivers receiving' a half or about a half of the channels.

These receivers are of the simplesuperheterofv dyne kind and comprise under exclusion of' the high frequency amplifying stage, a mixer discharging. into. m/2 intermediate'f-'requency ampliers regulated so as to operate on diiferent'- intermediate frequencies. f

The first receiver receives the lower frequencies and is provided with a local oscillator which* oscillates at a frequency below the lowest" fre'- quency to be received and conversely the second.

frequencies is' provid'ed with a local oscillator which oscillates at a frequency which is higher than the highest frequency to be received.

It is therefore advisable to ixthev value of the.

' lowest of the intermediate frequencies at reception forthe onevorthe other of. the receiversthese; frequencies corresponding to' the first and last channel, respectively, the other intermediate. fre.- quencies resulting for the one or. other, ofi the receivers ofv this. lowest value.l

In noting that the parasiticy waves.. of. signifi-n cant amplitude cover the band: 3M or thev values:i of. -S tov +25' itis necessary to-avoid that-,paraesitics; atl -fS on +2S havel frequencies: coincident Orr and

By placing them at values and f S -l- 1 S+ 2 a protection against the parasitic waves is accomplished consisting to a frequency interval equal to the predetermined frequency difference, at the same time preserving the lowest compatible intermediate frequencies. This means placing the value of the rst intermediate frequency at half the frequency of the useful band augmented by the predetermined frequency diiference.

.It has not yet been stated herein whether the nominal frequencies of the channels correspond to the weakened carriers or to the retained side bands. It is preferable that these correspond to the retained side bands.

On the other band it is obvious that the intermediate frequencies of the receivers should have such a selectivity curve that the carrier waves reduced at the emission with respect to the retained side band areY on the contrary increased with respect to latter at the reception.

There is hereafter described a non limitative example of an embodiment comprising 6 channels.

All the elements being known per se, a single line schematic will be sufncient for the understanding (Fig. 1).

Each channel comprises at the emission a microphone Mz', a frequency transposition stage T fed by an oscillator q regulated to the transposition frequency of the channel, and a band filter F covering the range of the transposed frequencies, 1p. The transposed currents flow to a modulator Mo to which is also applied an oscillator P regulated to the intermediate carrier frequency corresponding to this channel; the currents of the carrier P modulated in amplitude are amplified by stage A having a response curve as function of the frequency being such that the carrier is attenuated with respect to the side maintained band (circuits tuned to the side band).

The different channels are identically equipped but the oscillators :p and P produce frequencies having different values, and the band nlters F allow e different bands to pass. hence their designation by a subscript.

A The mixing of the different channels is effected at the output of the ampliiiers A and the spectrum thus constituted is applied to a single band transmitter E which transposes it to ultra-high frequencies, for example 3Go to 400 mc., only the upper band being kept.

Only the rst and last channel is shown in solid lines. For 6 channels the values of cpi to pe can be 80-84--88--92-96-100 kilocycles and the values of (P1-H01) (P2-H92) etc. (upper band being kept) are between 15.5 and 23 megacycles with successive frequency distances similar to the numbers 3-5-'7-6-4- The predetermined frequency diiierences is therefore 300 kilocycles and the occupied band 7.5 megacycles. It should be noted that the ratio is less than 3/2.

The aerial, or more exactly the aerial feeder operates by the coupling loops or better across the tuned pots the frequency chargers M1 and M2 operated themselves by heterodynes H1 and H2.

The receiver R1 associated with I-Ii and M1 is destined for the reception of the three channels having lowest frequency, therefore here the channels I, II, III and the receiver R2 associated with H2 and Mz the three channels having the highest frequencies.

The output of M1 feeds the three intermediate frequency amplifiers MF1, MFz, MP3 and the outnltered in filters Fe identical with those of the emission and finally speech is re-established clearly by subjecting it in T to the same transposition as at the emission. Finally it is received in the head gear C.

According to what has been said hereinabove the lowest of the intermediate frequencies admissible at the reception should be at least equal to half the frequency of the occupied band augmented by the predetermined frequency diicrence, therefore 3.9 megacycles. The other intermediate frequencies are deduced from that and will be respectively 4.8 and 6.3 for one receiver and 5.1 and 6.9 mc. for the other. These values correspond to the side bands transmitted effectively.

It is seen that according to this concept it is sufiicient to change the frequencies of the quartz crystals of the transmitter E and also those of the crystals of the heterodynes H1 and Hz, in order to change the operating waves, it is then sufficient to retune the ultra-high frequency circuits only to the new waves.

With the restriction heretofore mentioned that several transmitters never function on the same channel the capacity of the network can be increased by subdividing the channels into two channels according to the arrangement represented in Fig. 2 which shows the equipment of one channel for emission and reception.

At emission the modulator Mn receiving the carrier wave P1, if it relates to channel I, is operated by transposed speech currents from band lters Foi and Fgo'1 established for neighbouring transposition frequencies p1 and (pi.

At reception the detector D feeds in parallel band filters F101 and Fok and speech is clearly re-constituted by transposition by means of frequencies p1 and oi. For the doubled channel I transposition frequencies ci and 1.

'Z6 and 80 kilocycles.

According to this modication each channel represents in fact a two channel multiplex with frequency subdivision and no supplementary cause for interference is introduced as a consequence, only the modulation spectrum of the channel being doubled.

I claim:

l. A multichannel radio-electrical communication system having a plurality of stations operating with ultra-short waves. each of said stationscomprising, in combination, lineans- :for transforming voice frequency signals A,into audio frequency bands associated,,'respectively, with fthe channels'of the communicationvsystem; :aplurality of sources -of intermediate frequency -associated, respectively, with the-channels of the com municationsystem, said intermediate frequencies differing by amounts'beingdifferentqfrom one another 'and being integral ,multiples of a predetermined frequency difference.; iineans :for amplitude-modulating said intermediate frequencies associated, respectively, with the channels, respectively, by said voice frequency bands associated with the channels so as to obtain intermediate frequencies and two side bands for each of said intermediate frequencies; means for suppressing one of said side bands of each intermediate frequency and attenuating said intermediate frequencies so as to retain the otheriofsaid side bands yof said intermediate frequencies, said retained side bands associated with v,the channels ofthe communication system being, respectively, separated from oneanother byamountsdiffering from one another, the smallestof rsaid amounts being equal to the .product of said predetermined frequency difference and an integer being-equal to one of and m being the "total knumber of channels of the communication system, the largest of said amounts being equal to the product of said predetermined frequency difference and said integer augmented by (7n-2); `a single ultra-high frequency transmitter operating with one side band only; means for amplitude-modulating said sin gle ultra-high frequency :transmitter by a combination of said retained side bands andv said attenuated intermediate frequencies; -a rst receiver; a second receiver, each of said receivers serving for lreceiving `half the total number of the `frequencies assigned, respectively, to the channels; a irstlocal oscillator cooperating with said first receiver and generating a lfrequency lower than Ithe lowest frequency to 'be received; a second local oscillator cooperating with l'said second receiver and generating a frequency higher than the highest frequency to 'be received; means for mixing said frequencies generated by said rst and second oscillators with said frequencies received, respectively, by said vfirst and second receivers so vas to generate a first intermediate 'frequency 'and a second intermediate frequency; means for amplifying said first vand second intermediate frequencies; and means for demodulating said vamplified first and second intermediate frequencies so as to obtain `two oscillations having frequencies differing 'from each otherby a quantity equal to said predetermined frequency difference.

2. A multichannel radio-electrical communication system havinga plurality of stations operating with ultra-short waves, each of said stations comprising, in combination, means for transforming voice frequency signals into audio frequencybands associated, respectively, with the channels of the communication system; a plurality of sources of intermediate frequency associated, respectively, with the lchannels yof the communication system, said intermediate frequencies l@ diieringby Aamounts being different from .oneganotherand being integral multiples of a predetermined frequency diiference; means for amplitilde-modulating said intermediate frequencies associated, respectively, with the channels, respectively, lby said voice frequency bands associated with the channels so as to obtain intermediate frequencies and two side bands for each of said intermediate frequencies; means for suppressing -oneof said side bands of each intermediate frequency and -attenuating said intermediate frequencies so as to retain the other of said side bands of said intermediate frequencies, said retained side bands associated with the channels of the communication system being, respectively,

separated from one another by amounts diering from one another, the smallest of said amounts being equal to the product of said predetermined frequency difference and an integer being equal to one of and m being the total number of channels of the communication system, the largest of said amounts being equal to the product of said predetermined frequency difference and said integer augmented by (1n-2), the integral multiples of said predetermined frequency difference lying between said smallest and largest of said amounts being assigned in any order to the intermediate channels of the communication system; a'single ultra-high frequency transmitter operating -with one side band only; meansfor amplitude-modulating said single .ultra-high frequency transmitter by al combination of said retained side bands and said attenuated intermediate frequencies; a first receiver; a secondreceiver, each of saidreceivers serving for receiving "half the total'nuin-I ber of the frequencies assigned, respectively, to the channels; a first local oscillator cooperating with said rst receiver and generating .a frequency lower than the lowest frequency to be received; a second local oscillatorcooperating with said second receiver and generating a frequency higher than the highest frequency to be received; means for mixing said frequencies generated vby said first and second oscillators with said frequencies received, respectively, by said first and second receivers so as to Lgenerate a first intermediate frequency and a second intermediate frequency; means for amplifying said first and second intermediate frequencies; and means for demodulating said amplified rst and second intermediate frequencies so as .to obtain two oscillations having frequencies differing from each other by a lquantity equal to said predetermined frequency difference.

3. A multichannel radio-electrical communication system having a plurality of stations operating with ultra-short Waves, each of said stations comprising, in combination, means for transforming voice frequency signals into audio frequency bands associated, respectively, with the channels of the communication system; a plu-` rality `of sources of intermediate frequency associated, respectively, with the channels of the communication system, said intermediate freamplitude-modulating said intermediate frequencies associated, respectively, with the channels, respectively, by said voice frequency bands associated with the channels so as to obtain intermediate frequencies and two side bands for each of said intermediate frequencies; means for suppressing one of said side bands of each intermediate frequency and attenuating said intermediate frequencies So as to retain the other of said side bands of said intermediate frequencies, said retained side bands associated with the channels of the communication system being, respectively, separated from one another by amounts differing from one another, the smallest of said amounts being equal to the product of said predetermined frequency difference and an integer being equal to one of m being the total number of channels of the communication system, the largest of said amounts being equal to the product of said predetermined frequency derence and said integer augmented by (vn-2); a single ultra-high frequency transmitter operating with one side band only; means for amplitude-modulating said single ultra-high frequency transmitter by a combination of said retained side bands and said attenuated intermediate frequencies; a iii-st superheterodyne receiver; a second superheterodyne receiver, each of said receivers serving for receiving half the total number of the frequencies assigned, respectively, to the channels; a first local oscillator cooperating with said first receiver and generating a frequency lower than the lowest frequency to be received; a second local oscillator cooperating with said second receiver and generating a frequency higher than the highest frequency to be received; means for mixing said frequencies generated by said first and second oscillators with said frequencies received, respectively, by said first and second receivers so as to generate a first intermediate frequency and a second intermediate frequency; means for amplifying said first and second intermediate frequencies; and means for demodulating said amplified first and second intermediate frequencies so as to obtain two oscillations having frequencies differing from each other by a quantity equal to said predetermined frequency difference.

4. A multichannel radio-electrical communication system having a plurality of stations operating with ultra-short waves, each of said stations comprising, in combination, means for transforming voice frequency signals into audio frequency bands associated, respectively, with the channels of the communication system; a plurality of sources of intermediate frequency associated, respectively, With the channels of the communication system, said intermediate frequencies differing by amounts being diiierent from one another and being integral multiples of a predetermined frequency difference; means for amplitude-modulating said intermediate frequencies associated, respectively, with the channels, respectively, by said voice frequency bands associated with the channels so as to obtain intermediate frequencies and two side bands for each of said intermediate frequencies; means for suppressing one of said side bands of each intermediate frequency and attenuating said intermediate frequencies so as to retain the other of said side bands of said intermediate frequencies, said retained side bands associated with the channels of the communication system being, respectively, separated from one another by amounts differing from one another, the smallest of said amounts being equal to the product of said predetermined frequency difference and an integer being equal to one of m being the total number of channels of the communication system, the largest of said amounts being equal to the product of said pre-` determined frequency diiference and said integer augmented by (1n-2), the integral multiples of said predetermined frequency difference lying between said smallest and largest of said amounts being assigned in any order to the intermediate channels of the communication system; a single ultra-high frequency transmitter operating with one side band only; means for amplitude-modulating said single ultra-high frequency transmitter by a combination of said retained side bands and said attenuated intermediate frequencies; a first superheterodyne receiver;` a second superheterodyne receiver, each of said receivers servl ing for receiving half the total number of the A ceived, respectively, by said first and second i receivers so as toV generate a first intermediate frequency and asecond intermediate frequency; means for amplifying said first and second intermediate frequeneies; and means for demodulating said amplified first and second intermediate frequencies so as to obtain two oscillations having frequencies differing-from each other by a quantity equal to said predetermined frequency difference.

' 5. A multichannel radio-electrical communication system having a plurality of stations operating with ultra-short waves, each of said stations comprising, in combination, means for transforming voice frequency signals into audio frequency bands associated, respectively, with the channels of the communication system; a plurality of sources of intermediate frequency associated, respectively, with the channels of the communication system, said intermediate frequencies differing by amounts being different from one another and being integral multiples of a predetermined frequency diiference; means for amplitude-modulating said intermediate frequencies associated, respectively, with the channels, respectively, by said voice frequency bands associated with the channels so as to obtain intermediate frequencies and two side bands for each of said intermediate frequencies; means for suppressing one of said side bands of each interme- Y diate frequency and attenuating said intermediate frequencies so as to retain the other of said 13 yside hands of said intermediate frequencies, :said

.retained vside .bands associated with the channels :m being the total number of channels of the lcorn;- bination system, the largest of said amounts -being equal to the product of `said predetermined frequency difference and said integer augmented by (m-2.).; a single ultra-high frequency transmittel` operating `with one side band only; means for `amplitude-modulating said single ultra-high frequency transmitter by a Vcombination of said retained side bands and said attenuated intermediate frequencies; a first receiver; a Ysecond receiver, each of said receivers serving for receive ing half the total number of the frequencies assigned, respectively, to the channels; a first local oscillator cooperating with said first receiver andgenerating a frequency lower than the lowest frequency to be received; a second local oscillator cooperating with said second receiver and generating a frequency higher than the highest fre-l quency to be received; .means .for mixing said frequencies generated by said `first and second oscillators with said frequencies received, respectively, by said rst and second receivers so as to generate a iirst intermediate frequency anda secnd intermediate frequency, said first intermediate frequency being equal to half the `occupied band width augmented by said predetermined frequency difference; means for amplifying said rst and second intermediate frequencies; and means for demodulating said amplified iirst and second intermediate frequencies so 'as to obtain tw'ooscillations having frequencies differing from each other by a quantity equal to said predetermined frequency difference.

6. A multichannel radio-electrical communication system having a plurality of stations operating with ultra-short Waves, each of said staa tions comprising, in combination, means for transforming voice 'f'rerniency signals inte audio frequency bands associated, respectively, with the channels of the communication system; a plurality of sources of intermediate frequency associated, respectively, with the channels of the communication system, said intermediate frequencies differing by amounts being different from one another and being integral multiples of a predetermined frequency difference; .means for amplitude-'modulating said intermediate frequencies associated, respectively, with the channels, respectively, by said voice frequency bands associated with the channels so as to obtain intermediate frequencies and two side bands for each of said intermediate frequencies; means for suppressing one of said side bands of each intermediate frequency and attenuating said intermediate frequencies so as to retain the other of said side bands of said intermediate frequencies, said retained side bands associated with the channels of the communication system being, respectively, separated from one another by amounts differing from one another, the smallest of said amounts being equal to the product of said .pre-

determined frequency diiference and 1an integer beiner equal to one of (1n- 2Min* 3) 6 and m being the total number of channels of the com- .munication system, the largest of said amounts being equal to the product of said predetermined frequency diiference and said yinteger augmented by (m42), the integral multiples of said pre'- determined frequency difference lying between said smallest and largest of said amounts being assigned in any order to the intermediate channels of the communication system; a single ultrahi'gh frequency transmitter operating with one side band only; means for amplitude-modulating said single ultra-high frequency transmitter by a combination cf said retained side bands and said attenuated intermediate frequencies; .a first receiver; a second receiver, each of said receivers serving for receiving `half the total nume ber of the frequencies assigned, respectively, to the channels; a first local oscillator 'cooperate ing with said iirst receiver'and generating a frequency lower than the lowest frequency to .be received; a second .local oscillator cooperating with said second receiver and generating a frequency higher than the highest frequency to be received; means for mixing said frequencies generated by said first and second oscillators with said frequencies received, respectively, by said first and second receivers so as to generate a first intermediate frequency and a second intermediate frequency., said first intermediate frequency being equal to half the occupied band Width augmented by said predetermined frequency difference.; means for amplifying said first and second intermediate frequencies; and means for deniodulating said amplified first and second intermediate frequencies so as tov obtain two oscillations having frequencies differing from other by :a quantity equal to said predetermined frequency idinerence.

fi, .A multichannel :radicelectrical communication system having a plurality of .stations `oper-- ating with ultra-short Waves, each of said' stations' comprising, vin combinati-on, means for transforming `voice frequency signals into audio frequency bands associated, respectively, `with the `channels of the communication system; a plurality of ysources of intermediate frequency associated, respectively, with the lchannels ofthe communication system, said intermediate fre# quen-cies diiiering by `amounts Vbeing different from one 'another 'and vbeing integral multiples of a predetermined 'frequency difference; ici-leans for amel-itude-'modulating Vsaid intermediate :frequencies associated, respectively, Wit-nth@ channels, respectively, by said 4voice frequency bands associated with `the channels .so as to .obtain in termedia'te frequencies and vtwo side Vbands for each of said intermediate frequencies; means for suppressing one of said side bands of each intermediate frequency and attenuating said intermediate frequencies so as to retain the other of said side ban-ds of said intermediate frequencies, said retained side bands associated with the channels of the communication system being, respectively, separated from one another by amounts differing from one another, the smallest of said amounts being equal to the product of said predetermined frequency diiference and an integer being equal to one of m being the total number of channels of the'communication system, the largest of said amounts being equal to the product of said predetermined frequency difference and said integer augmented by (1n-2) a single ultra-high frequency transmtter operating'with one side band only; means for amplitude-modulating said single ultra-high frequency transmitter by a combination of said retained side bands and said attenuated intermediate frequencies; a iirst superheterodyne receiver; a second superheterodyne receiver, each of said receivers serving for receiving half the total -number of the frequencies assigned, respectively, to the channels; a first local oscillator cooperating with said first receiver and generating a frequency lower than the lowest frequency to be received; a second local oscillator cooperating with said second receiver and generating a frequency higher than the highest frequency to be received; means for mixing 'said frequencies generated by said first and second oscillators with said frequencies received, respectively, by said first and second receivers so as to generate a rst intermediate frequency and a second intermediate frequency, said first intermediate frequency being equal to half the occupied band width augmented by said predetermined frequency difference; means for amplifying said first and second intermediate frequencies; and means for demodulating said amplined first and second intermediate frequencies so as to obtain two oscillations having frequencies differing from each other by a quantity equal to said predetermined frequency difference.

'8. A multichannel radio-electrical communication system having a plurality of stations operating with ultra-short waves, each of said stations comprising, in combination, means for transforming voice frequency signals into audio frequency bands associated, respectively, with the channels of the communication system; a plurality 'of sources of intermediate frequency associated, respectively, with the channels of the communication system, said intermediate frequencies differing by amounts being different from one another and being integral multiples of a predetermined frequency difference; means for amplitude-modulating said intermediate frequencies associated, respectively, with the channels, respectively, by said voice frequency bands associated with the channels so as to obtain intermediate frequencies and two side: bands for each of said intermediate frequencies; means for suppressing one of said side bands of each intermediate frequency and attenuating said intermediate frequencies so as to retain the other of said side bands of said intermediate frequencies, said retained side bands associated with the channels of the communication system being, respectively, separated from one another by amounts differing from one another, the smallest of said amountsbeing equal tothe product of said predetermined frequency difference and an integer being equal to one of m being the total number of channels of the communication system, the largest of said amounts being equal to the product of said predetermined frequency difference and said integer augmented by (1n-2), the integral multiples of said predetermined frequency difference lying between said smallest and largest of said amounts being assigned in any order to the intermediate channels of the communication sys. tem; a single ultra-high frequency transmitter operating with one side band only; means for amplitude-modulating said single ultra-high frequency transmitter by a combination of said retained side bands and said attenuated inter-k mediate frequencies; a first superheterodyne receiver; a second superheterodyne receiver, each of said receivers serving for receiving half the total number of the frequencies assigned, respectively, to the channels; a first local oscillator cooperating with said first receiver and generating a frequency lower than the lowest frequency to be received; a second local oscillator cooperating with said second receiver and generating a frequency higher than the highest frequency to be received; means for mixing said frequencies generated by said first and second oscillators with said frequencies received, respectively, by said first and second receivers so as to generate a rst intermediate frequency and a second intermediate frequency, said first intermediate frequency being equal to half the occupied band width augmented by said predetermined frequency difference; means for amplifying said rst and second intermediate frequencies; and means for demoduiating said amplified first and second intermediate frequencies so as to obtain two oscillations having frequencies dinering from eachother by a quantity equal to said predetermined frequency difference.

HENRI CHIREIX.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,361,488 Osborne Dec. '7, 1920 1,361,522 Espenschied Dec. 7, 1920A 1,559,867 Griggs Nov. 3, 1925 1,641,431 Horton Sept. 6, 192'? 2,284,706 Wiessner et al June 2, 1942 2,298,409 Peterson Oct. 13, 1942 

